More significantly, the move has boosted blackgrass control to 98%. That should help wind down soil seed banks, so eventually even less may need to be spent to keep crops weed-free.

For 17 years Mr Butler, a LEAF demonstration grower, has based cereal blackgrass control on IPU mixed with either diflufenican (DFF), tri-allate or pendimethalin.

But repeatedly poor control meant about a third of his cereal area needed follow-up herbicide each spring. "It has been patchy. Sometimes we get good results, but we have had up to 300 plants a sq m," says Mr Butler. "We have had fop and dim resistance on some fields, but I only grow first wheats which helps a lot. We also use quite a bit of Sting after the breaks."

Soil types range from clay to sand and gravel. "They are very variable. We plough and use minimal cultivations about half and half."

For 1998 harvest his average herbicide spend was £37.75/ha. That included over-spraying 35% of the winter wheat in spring to control surviving blackgrass, and the cost of the extra spraying operation.

For the first time last autumn, Mr Butler treated all 161ha (398 acres) of his winter wheat with Hawk (clodinafop + trifluralin) plus adjuvant oil, a treatment previously used only in early spring.

Herbicide outlay fell by £4.50/ha (£1.82/acre) to £33.27/ha (£13.46/acre), and blackgrass control, averaging 98% as judged by eye, was the best ever on the farm, he says.

"We had been using full rate IPU. But blackgrass was still getting away, particularly in wet autumns. We were having to go back in spring with either Topik (clodinafop), Cheetah (fenoxaprop), or some early spring Hawk, to clear up. We also tried patch spraying, but it was not often successful."

Despite the latest cost cuts, he reckons there may be scope for more. Three weather-driven alternative Hawk programmes suggested by David Blazey were tried last year, but one could be trimmed further.

"Last year we had intended to use low rate IPU/DFF all over, but the weather stopped us," says Mr Butler.

Hawk at 2 litres/ha plus 1 litre/ha of adjuvant oil in mid-November was eventually the core component. In the cheapest programme, costing £29.92/ha (£12.10/acre), it was followed with HBN + mecoprop-P to boost broad-leaved weed control. This went on with early spring growth regulator.

Next cheapest, was Hawk + oil tank-mixed with IPU at 2 litres/ha for broad-leaved weeds, again in mid-November. That also worked out cheaper than the previous years strategies at £34.72/ha (£14.05/acre).

Most expensive, though, was a sequence of the originally planned 2 litres/ha of IPU + 0.4 litres/ha of DFF in mid-October followed by the Hawk/oil mix for blackgrass. That cost £39.48/ha (£15.98/acre), but Mr Butler believes savings are possible. "We used the sequence on early drilled wheat because we were worried late germinating blackgrass might get away if it turned wet. The lesson we learned is we need not have worried. Hawk at the two- to three-leaf stage of the blackgrass did a good job.

"Results were very similar with all programmes and we had about a 10% reduction in costs. Previously, after IPU, we would still have patches of blackgrass left over that reduced yield. If I had controlled these better my overall yields would have increased."

As well as improving yields Mr Butler hopes that repeated 98% control will gradually help reduce blackgrass seed banks in the soil. Ultimately, the five-year aim is to trim back further on herbicide costs.

The only benefit from adding IPU comes from broad-leaved weed control, he notes. "Hawk fits well with ICM. It is largely contact so there is less danger of it leaching into watercourses."

He is not unduly concerned that relying on the fop may aggravate resistance. "If I was growing continuous wheat I might have to change. It might become a problem in five years time, but we will probably have new chemistry by then." &#42